Some faucets suffer from the effects of cross-contamination. The transfer of germs from one user to another can occur when a user touches a handle that enables the flow of water. Cross-contamination may result from hand-to-mouth, hand-to-nose, and hand-to-eye contact. An awareness of such contamination can create a reluctance to touch a fixture, which does not promote or preserve good hygiene.
To minimize the risk of transferring germs, some faucets use hands-free methods to control water flow. In these systems a passive sensor is used to detect a user. Once a user is detected, water flows for a fixed period of time.
A problem with some hands-free faucets is their inability to be turned on or off or to sustain a continuous water flow when a user is not detected. Because all sources of water possess naturally occurring contaminants, sometimes it is necessary to flush faucets and waterlines. Requiring a user to stand in front of a spout to flush a hands-free faucet can be time consuming and costly. The short periods of time that these hands-free faucets allow continuous water flow can also be inadequate as short periods of uninterrupted water flow will not always purge faucets of contaminants. Ironically, some automatic faucets used to prevent the spread of germs are more difficult to purge of water borne bacteria because a user is required to normally cause flow.